(1) Field of the Invention
This invention relates to an improved impact or bang plug assembly comprising a plug and a mating crossbar, wherein the crossbar is reliably inhibited from separating from the plug before installation and use in a workpiece. More specifically, the crossbar is retained in diametrically opposed slots in the plug sidewalls by shear lip means formed in the crossbar adjacent and outside the sidewalls, whereby the crossbar is captured inside the slots and retained with the plug by the shear strength of the material forming the crossbar.
(2) Discussion of the Prior Art
Impact or bang plug assemblies are known in the prior art for engaging a workpiece to close or seal an aperture formed therein. A typical application for a bang plug is closing off circular openings in the sheet metal of an automobile underbody, which openings are cut so that the whole body may be dipped in a paint bath and excess paint residue will drain out through the openings.
The typical bang plug assembly comprises a circular plug of metal for insertion into a circular opening. The plug may be shaped like a shallow, thin, flat-bottomed bowl with a relatively flat bottom wall portion for extending across the aperture and adjoining sidewall portions for mating with the workpiece boundary defining the aperture.
An elongated crossbar comprising an angled strip of metal is positioned inside and above the plug bottom in diametrically opposed slots formed in the plug sidewall adjacent the bottom wall, with the two opposite ends of the crossbar protruding through these slots only a relatively short distance. The two opposing ends of the crossbar are retained inside the slots and therefore inside the plug, while the angled portion of the crossbar midway between the two ends is poised above the plug bottom, the total length of the crossbar being substantially greater than the diameter of the plug. The plug is placed in the sheet metal opening, and the crossbar is typically struck with a hammer in a direction toward the plug bottom, or downwardly. The ends of the crossbar are forced out through the slots as simultaneously the angled portion of the crossbar is forced downward, is straightened, and comes to rest on the bottom wall or landing platform of the plug. The crossbar ends, which are suitably curved, are thereby driven or extended out through the slots into engagement with the underside of the sheet metal workpiece adjacent the aperture to lockingly retain the plug in place.
Before the plug assembly is installed and the crossbar driven into place, the crossbar sits relatively loosely in the plug and is typically retained in the slots by circular depressions or dimples formed in the crossbar material just on the outer side of the plug sidewalls. These dimples are designed to restrain the crossbar ends from being pulled or otherwise deformed back through the slots.
The spring action in the dimple transverse to the direction of travel of the crossbar through the slot permits the crossbar material in the region of the dimple to flex or be momentarily displaced as the dimple passes through the slot. There is a specific spring constant associated with the dimple that permits this flexing to take place. This spring or flexing action may permit the dimple to be pulled or forced back through the slot, thereby possibly resulting in the undesirable separation of the crossbar from the plug as the plug assemblies are shipped in mass or otherwise handled prior to installation.
A particular shortcoming of this prior art bang plug assembly is that, notwithstanding the dimples, the crossbar has a tendency to separate from the plug before installation and use. This is a substantial problem for both the bang plug manufacturer and also the end user, because a bang plug without a matching crossbar is virtually useless and a bang plug with a partially detached crossbar is a nuisance.